Measuring Raman Spectra Research Articles

Twist-angle-dependent optical behaviors of excitons in twisted bilayer MoS2 at low temperature

Twisted bilayers of two-dimensional materials provide a powerful and attractive platform to control band structure and tailor optical properties since the twist angle θ between the bilayer has been shown to be a critical parameter in engineering the moiré potential. Here, we demonstrate the θ-driven effects on excitons in twisted bilayer MoS2 (tBLMs) by measuring photoluminescence (PL) spectra. The localized state exciton between 1.70 eV and 1.80 eV is observed at 7 K with properties periodically modulated by θ. The θ is also a crucial factor affecting direct excitons. Furthermore, the phonon around 410 cm−1 has a θ dependence similar to excitons by measuring Raman spectra. The localized stacking patterns, the recombination of excitons, and the phonon-exciton interactions are confirmed in tBLMs. Our work provides the help to investigate the new quantum phenomena of tBLMs by optical methods and provides possibilities to manipulate the emission of excitons in tBLMs.

Estimation of cadaveric age in crime scenes using Raman spectroscopy

The number of unidentified corpses has been increasing in recent years. There is a need for an objective and readily applicable method to estimate age, which is important information for identification. In previous reports, we reported that the protein folding ratio (RPF) of skin, as measured by Raman spectroscopy using cross sections of skin samples, is highly correlated with age. In this study, we investigated the possibility of estimating age by measuring Raman spectra from the skin surface of cadavers using a portable device.The resultant intercept, slope, and root mean square error were 97.9, – 63.7 (p < 0.0001), and 11.68, respectively. We evaluated this regression formula by using 10-fold cross-validation, resulting in a coefficient of determination of 0.51. The portable Raman spectrometer may be of assistance in estimating age at death of corpses at the scene of discovery.

Multipoint Raman Spectrometer Based on a Time-Resolved CMOS SPAD Sensor

The potential of in-line Raman spectrometers for process monitoring applications has been shown for many industrial processes, but in most cases, only one measurement point has been monitored by one spectrometer. In this letter, we describe and demonstrate a novel, time-resolved method for measuring Raman spectra and fluorescence lifetimes from multiple points using a single excitation source and a single spectrometer. This technique is based on a combination of a time-resolved CMOS SPAD (single-photon avalanche diode) line sensor and a fitting optical light guiding system. The line sensor is designed to make multiple individual measurements at intervals of tens of nanoseconds and the optical light guiding system, in turn, produces matching temporal differences for optical signals from different measurement points. Thereby, signals from different points are distinguished in the time domain. A combined Raman and fluorescence lifetime monitoring of two measurement points was demonstrated with an oil-ethanol emulsion sample.

Arduino-based wireless spectrometer: a practical application

We provide a technical report on designing an Arduino-based wireless spectrometer using an old spectrometer. The designed spectrometer is environmentally friendly and cost-effective and can be used in physical and analytical laboratories. The Arduino-based wireless spectrometer enables students to understand the fundamental theory of spectroscopy and wireless communication among instruments. The rotating motions of the mirror and grating turret inside the spectrometer are controlled by a pre-written source code based on the Arduino program. This procedure can give an insight into spectroscopic analysis and telecommunication skills using computer-based software. Using our customized spectrometer, we measure Raman spectra from a silicon wafer, 4-nitrobenzenethiol, and rhodamine 6G, which serve as representative Raman probe molecules. From our results, we conclude that our approach provides intuitions for wide applications of Arduino-based chemical instruments.Graphical

Time-gated Raman spectroscopy of recovered plastics

Raman spectroscopy is a powerful non-destructive technique for the identification and characterization of plastics, but a major shortcoming of this technique is that environmental weathering, dyes, and additives in the material can generate a strong fluorescence background that overwhelms the Raman scattering. Here, we demonstrate that time-gated Raman spectroscopy can be used to successfully reduce the fluorescence signal and measure Raman spectra of recovered plastics. Time-gating removes a significant amount of background signal from the Raman spectra such that the polymers and color additives can be identified using similar measurement times compared to continuous-wave Raman spectroscopy. Examples of this are shown for a small subset of samples recovered from Hawaiian marine environments and a nonweathered commercial plastic. Time-gated Raman spectroscopy can also be used to characterize samples that are black in color due to carbon-based additives like graphite, which can be challenging to characterize via other common vibrational spectroscopic techniques.

Influence of Raman spectra measurement conditions on the dating results of writing compositions

When establishing the age of a document using spectral methods, the result is influenced not only by the storage conditions, but also by the methods of measuring the spectra and mathematical processing of the results. This work analyzes the influence the modes of measuring Raman spectra have on the result of measuring the writing composition spec-tra. The analysis area includes the correlation coefficients of the full spectral matrices as a criterion for the reliability of the determination date. The influence of focusing accuracy, correctness of subtraction of the baseline, sample irradiation time, and varying the number of repetitions is investigated. In the study, chemometric tools for the analysis of Raman spectra were also applied. The influence of mathematical spectra processing shows that the components PC4, P5, and PC6 are most closely related to the shelf life, although they do not make the maximum contribution to the variance in the system. Taking into account all the requirements for measuring spectra, the PCA method applied to the Raman spectra of writing compositions allows clustering samples by manufacturer’s brands and by the sample shelf life.

Method for studying the photostability of solar cells based on organic-inorganic perovskites using a confocal spectrometer

A method for studying photosensitive structures using the example of studying the photodegradation and dark recovery of organic-inorganic perovskite solar cells is present. The method is based on the use of a confocal spectrometer to measure Raman spectra, photo- and electroluminescence spectra and kinetics, the kinetics of the short-circuit current and the open-circuit voltage under local exposure to monochromatic radiation. Raman spectra make it possible to establish the presence or absence of secondary phases, the formation of which is possible in photosensitive layers under the influence of light. The photoluminescence spectra enable to reveal the single-phase nature of the object under study. Mapping the intensity and position of the center of mass of the photoluminescence band in the plane of the object makes it possible to judge the spatial arrangement of the centers of non-radiative recombination of charge carriers, the distribution of the regions with the highest and lowest efficiency of the extraction of charge carriers by transport-acceptor layers and the spatial homogeneity of the chemical composition. Comparison of the electroluminescence spectra before and after light exposure allows revealing the formation of non-radiative recombination centers in the photoabsorbing layer and at interfaces with the transport layers. Analysis of the kinetics of changes in the parameters of the photoluminescence band obtained by measuring the short-circuit current and the open-circuit voltage makes it possible to establish the dominant photoinduced processes leading to a change in the intensity of the photoluminescence band.

Gold Nanostars Bioconjugation for Selective Targeting and SERS Detection of Biofluids.

Gold nanoparticles (AuNPs) show physicochemical and optical functionalities that are of great interest for spectroscopy-based detection techniques, and especially for surface enhanced Raman spectroscopy (SERS), which is capable of providing detailed information on the molecular content of analysed samples. Moreover, the introduction of different moieties combines the interesting plasmonic properties of the AuNPs with the specific and selective recognition capabilities of the antibodies (Ab) towards antigens. The conjugation of biomolecules to gold nanoparticles (AuNPs) has received considerable attention for analysis of liquid samples and in particular biological fluids (biofluids) in clinical diagnostic and therapeutic field. To date, gold nanostars (AuNSts) are gaining more and more attention as optimal enhancers for SERS signals due to the presence of sharp branches protruding from the core, providing a huge number of “hot spots”. To this end, we focused our attention on the design, optimization, and deep characterization of a bottom up-process for (i) AuNPs increasing stabilization in high ionic strength buffer, (ii) covalent conjugation with antibodies, while (iii) retaining the biofunctionality to specific tag analyte within the biofluids. In this work, a SERS-based substrate was developed for the recognition of a short fragment (HA) of the hemagglutinin protein, which is the major viral antigen inducing a neutralizing antibody response. The activity and specific targeting with high selectivity of the Ab-AuNPs was successfully tested in transfected neuroblastoma cells cultures. Then, SERS capabilities were assessed measuring Raman spectra of HA solution, thus opening interesting perspective for the development of novel versatile highly sensitive biofluids sensors.

Standoff Raman spectroscopy for future Europa Lander missions

AbstractNear Infrared Mapping Spectrograph data from the Galileo spacecraft and cryogenic laboratory reflectance measurements on hydrated compounds identified the presence of mixtures of hydrous magnesium sulfate, sulfuric acid, and hydrogen peroxide on the surface of Europa. Standoff Raman spectroscopy is ideally suited for exploring terrestrial Europa analog sites and Europa because of its ability to unambiguously identify minerals, organic compounds, and biomarkers inside ice. In the present work, we evaluated the performance of a standoff Raman system at various distances by measuring Raman spectra of hydrogen peroxide, sulfuric acid, and hydrous sulfate minerals, which are predicted to be present on Europa's surface. To simulate Europa's surface environment, Raman spectra of MgSO4·7H2O, FeSO4·7H2O, gypsum (CaSO4·2H2O), dry ice (CO2‐ice), and polycyclic aromatic hydrocarbons (PAHs) naphthalene and anthracene inside crushed H2O‐ice, shaved H2O‐ice, and a clear H2O‐ice block have also been measured. The PAHs were selected in this study because of their presence in the interstellar medium, comets, and meteorites. The results show that it will be possible to map out the non‐ice components on the surface and subsurface of Europa analog sites and Europa up to a distance of 120 m from a static lander and to a depth of ~10 cm inside ice.We have evaluated the performance of a standoff Raman system at various distances by measuring Raman spectra of hydrogen peroxide, sulfuric acid, and hydrous sulfate minerals, which are predicted to be present on Europas surface. To simulate Europas surface environment, Raman spectra of MgSO4·7H2O, FeSO4·7H2O, gypsum (CaSO4·2H2O), dry ice (CO2‐ice), and polycyclic aromatic hydrocarbons (PAHs) naphthalene and anthracene inside crushed H2O‐ice, shaved H2O‐ice, and H2O‐ice block have been measured.

Broadband Impulsive Stimulated Raman Scattering Based on a Chirped Detection.

In impulsive stimulated Raman scattering, vibrational oscillations, coherently stimulated by a femtosecond Raman pulse, are monitored in real time and read out as intensity modulations in the transmission of a temporally delayed probe pulse. Critically, in order to retrieve broadband Raman spectra, a fine sampling of the time delays between the Raman and probe pulses is required, making conventional ISRS ineffective for probing irreversible phenomena and/or weak scatterers typically demanding long acquisition times, with signal-to-noise ratios that crucially depend on the pulse fluences and overlap stabilities. To overcome such limitations, here we introduce the chirped-based impulsive stimulated raman scattering (CISRS) technique. Specifically, we show how introducing a chirp in the probe pulse can be exploited for recording the Raman information without the need to scan over the Raman-probe pulse delay. We then experimentally demonstrate with a few examples how to use the introduced scheme to measure Raman spectra.

Raman Scattering in Lithium Niobate and Lithium Tantalate Single Crystals and Ceramics

We have found conditions for high-speed measurements of Raman spectra of lithium niobate and lithium tantalate single crystals and ceramics. To measure Raman spectra, we used 180° scattering geometry and a minispectrometer equipped with an array detector. The Raman spectra obtained at two distinct orientations of the single crystals relative to the excitation beam direction have been shown to have different frequencies of transverse and longitudinal optical modes. The Raman spectra of the ceramics are mainly contributed by transverse optical modes.

Ultra-low background Raman sensing using a negative-curvature fibre and no distal optics.

Measuring Raman spectra through an optical fibre is usually complicated by the high intrinsic Raman scatter of the fibre material. Common solutions such as the use of multiple fibres and distal optics are complex and bulky. We demonstrate the use of single novel hollow‐core negative‐curvature fibres (NCFs) for Raman and surface‐enhanced Raman spectroscopy (SERS) sensing using no distal optics. The background Raman emission from the silica in the NCF was at least 1000× smaller than in a conventional solid fibre, while maintaining the same collection efficiency. We transmitted pump light from a 785‐nm laser through the NCF, and we collected back the weak Raman spectra of different distal samples, demonstrating the fibre probe can be used for measurements of weak Raman and SERS signals that would otherwise overlap spectrally with the silica background. The lack of distal optics and consequent small probe diameter (<0.25 mm) enable applications that were not previously possible.

Abstract A04: Unique Raman spectroscopic fingerprints of Burkitt non-Hodgkin lymphoma

Abstract Purpose: Raman spectroscopy (RS) is a noninvasive laser-based technique that provides a very high level of confidence in detecting various molecules through their vibrational modes. A monochromatic laser is used to excite a sample, and inelastic scattered light generated by the sample is used to measure Raman spectra of the sample. Because vibration modes of a molecule are very unique to the molecule, RS is sensitive and highly selective to the molecular composition of various chemicals including biologic tissues and cells. By using micro-Raman systems capable of measuring Raman spectra of single biologic cell, the objective of the study focused on identifying molecular differences between normal B-cells and Burkitt non-Hodgkin lymphoma (BNHL) cells, hypothesizing that unique RS fingerprints of BL could be identified with the overall goal to apply the information for novel diagnostic or treatment strategies. Methods: Normal B-cells were isolated from peripheral blood using a negative selection Robosep kit (EasySep Human B-Cell Isolation Kit, Stemcell Technologies, Cambridge, MA). BNHL cell lines (Ramos and CA46, ATCC, Manassas, VA), were cultured, washed, and resuspended in a 0.9% saline solution at a concentration of 1 x 106 cells/mL. The cells were mounted on a clean aluminum reflective slide and single cells were analyzed with a micro-Raman system utilizing a 785-nm laser excitation and an automated xyz microscope stage. Asymmetric Least Squares (AsLS) was applied to the spectral data (n=20 spectra per cell type) to obtain baseline spectra. Principal Component Analysis (PCA) followed by k-nearest neighboring (KNN) method was applied to analyze the variance in the spectral data and assess the diagnostic accuracy of the loadings from PCA. Results: The Raman fingerprints of normal B-cells and BNHL cells identified characteristic peak differences between the cell types, ranging from DNA/protein concentrations to saccharide bonds. These were further analyzed using AsLS and PCA. AsLS informed the PCA, which identified variances in the peaks that formed distinct clusters to differentiate normal B-cells from BL NHL cells. PCA effectively compiles the peaks, demonstrating that the first three components accounted for 97.45% of variance in the data. Several peaks were identified as the major contributors to the loadings, and some (e.g., 831, 1083, 1210, 1257, 1360, 1578, 1658 cm-1) were also reported as biomarkers of BNHL. The KNN on the PCs revealed that diagnostic accuracy was 100% and specificity was 100%. Conclusions: Raman fingerprints of normal B-cells versus BNHL cells demonstrated unique clustering of molecular changes that could potentially distinguish neoplastic cells from normal cells. As a novel and innovative tool, RS could contribute towards diagnostic resources and new paradigms for intervention for BNHL and other diseases. This study was supported by the St. Baldrick’s and McCabe Foundations and in part by NIH U54MD007584. Citation Format: Natalie Kamada, Robert Oda, Tiffany Shieh, Melissa Agsalda-Garcia, Tayro Acosta-Maeda, Anupam Misra, So Yung Choi, Eunjung Lim, Bruce Shiramizu. Unique Raman spectroscopic fingerprints of Burkitt non-Hodgkin lymphoma [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr A04.

Measurement of interfacial residual stress in SiC fiber reinforced Ni-Cr-Al alloy composites by Raman spectroscopy

Raman spectroscopy was used to measure Raman spectra of the inner SiC fibers and surface C-rich layers of SiC fibers, composite precursors and SiCf/Ni-Cr-Al composites. The residual stresses of the inner SiC fibers and surface C-rich layers were calculated, and the effect of the (Al + Al2O3) diffusion barrier layer on the interfacial residual stress in the composites was analyzed in combination with the interface microstructure and energy disperse spectroscopy (EDS) elements lining maps. The results show that the existence of (Al + Al2O3) diffusion barrier improves the compatibility of the SiCf/Ni-Cr-Al interface, inhibits the adverse interfacial reaction, and relieves the residual stress inside SiC fibers and at the interface of composite material. Heat treatment can reduce the residual stress at the interface. As the heat treatment time increases, the residual stress at the interface decreases.

Self-assembled quasi-hexagonal arrays of gold nanoparticles with small gaps for surface-enhanced Raman spectroscopy.

The fabrication and optical characterization of self-assembled arrangements of rough gold nanoparticles with a high area coverage and narrow gaps for surface-enhanced Raman spectroscopy (SERS) are reported. A combination of micellar nanolithography and electroless deposition (ED) enables the tuning of the spacing and size of the noble metal nanoparticles. Long-range ordered quasi-hexagonal arrays of gold nanoparticles on silicon substrates with a variation of the particle sizes from about 20 nm to 120 nm are demonstrated. By increasing the particle sizes for the homogeneously spaced particles, a large number of narrow gaps is created, which together with the rough surface of the particles induces a high density of intense hotspots. This makes the surfaces interesting for future applications in near-field-enhanced bio-analytics of molecules. SERS was demonstrated by measuring Raman spectra of 4-MBA on the gold nanoparticles. It was verified that a smaller inter-particle distance leads to an increased SERS signal.

Influence of silicate anions structure on desilication in silicate-bearing sodium aluminate solution

The structural changes of silicate anions in the desilication process with the addition of calcium hydrate alumino-carbonate were studied by measuring Raman spectra, infrared spectra and corresponding second derivative spectra. The results show that the desilication ratio in the solution prepared by the addition of sodium silicate (solution-SS) is much greater than that in the solution by the addition of green liquor (solution-GL), and low alumina concentration in the sodium aluminate solutions facilitates the desilication process. It is also shown that alumino-silicate anions in the solution-GL, and Q3 polymeric silicate anions in solution-SS are predominant, respectively. In addition, increasing the concentration of silica favors respectively the formation of the alumino-silicate or the Q3 silicate anions in the solution-GL or the solution-SS. Therefore, it can be inferred that the low desilication ratio in the silicate-bearing aluminate solution is mainly attributed to the existence of alumino-silicate anions.

Complementing Crystallography with Ultralow-Frequency Raman Spectroscopy: Structural Insights into Nitrile-Functionalized Ionic Liquids.

Functionalized ionic liquids are a subclass of ionic liquids that are tailored for a specific application. Structural characterization in both solid and liquid phases is central to understanding their physical properties. Here, we used ultralow-frequency Raman spectroscopy, which can measure Raman spectra down to approximately 5 cm(-1) , to study the structures and physical properties of 1-(4-cyanobenzyl)-3-methylimidazolium salts with five different anions. A comparison of the observed low-frequency Raman spectral patterns enabled us to predict the crystal symmetry of one of the synthesized salts for which single-crystal X-ray diffraction data were unobtainable. Real-time tracking of the low-frequency Raman spectral changes during melting revealed peak shifts indicative of different degrees of microscopic heterogeneity in the ionic liquids. The results show that our method provides a facile means that is complementary to X-ray crystallography, for obtaining structural information of ionic liquids.

Carrier transport spin–orbit dynamics in surface enhanced Raman shift of perovskite films

The unknown LSMO/ZnO spin-orbit dynamics and bandgap are presented by Mn partial wave state density of LaSrMnO3 and SRS spectroscopy.Raman active phonon in orthorhombic perovskite ZnO/La0.7Sr0.3MnO films are were focused by measuring Raman spectra in various scattering configurations. The LSMO spin state density is modified by Mn mixed valence state. The results show that the spin–orbit is caused by anomalies tilt of MnO6 octahedron and electrons hopped into the empty orbital states. The transfer of dx2−y2 orbits dynamics is in the background of the ferro-orbital order state of crystal stabilized d3z2−r2 orbit effect. The LSMO/ZnO displays magnetic and phononic scattering measurement. The kinetic energy gain achieved by the orbital competition, magnetic ordering, strong crystal field and charge order of energy band splitting. The LSMO/ZnO junction exhibits excellent junction ​antiferromagnetic/ferromagnetic phonon peaks and magnetoresistance behavior over the temperature range of 77–300 K.The significant energy band competition originates from the strong crystal splitting field and orbital canting.

Polythienylene–Vinylene Structure–Function Correlations Revealed from Resonance Raman Spectroscopy and Photocurrent Imaging

New structure–function correlations are revealed in poly(3-alkyl-thienylenevinylene) (P3ATV) derivatives using resonance Raman spectroscopy techniques. P3ATVs are prototype conjugated polymers that have received increased attention recently due to reports of efficient singlet fission following excitation of the lowest energy allowed (1Bu) excited state. Raman spectra are measured with excitation wavelengths resonant with the P3ATV 1Bu absorption line shape (∼450–750 nm) to probe geometrical rearrangements incurred in this initial excited state. Rich spectral features are resolved, namely, multiple overtone and combination progressions involving the main P3ATV symmetric skeletal stretching vibrational modes. We use a time-dependent wavepacket approach to calculate the Raman cross-correlation wavepacket overlap function for each displaced mode and their extent of displacement in the excited state. Fit parameters are checked by simulating optical absorption spectra that show good agreement with experimental absorption line shapes. Excitation wavelength-dependent Raman frequency dispersion and Raman excitation profiles of symmetric CC skeletal vibrations showed significant variation across the P3ATV absorption envelope and anomalously large enhancements for lower energy (longer wavelength) excitation, respectively. We demonstrate these behaviors are due to excitation of aggregated and amorphous P3ATV chains with distinct absorption and Raman signatures. This assignment was confirmed by measuring Raman spectra to selectively excite each limiting form and spectral decomposition of absorption line shapes using simulated absorption spectra of aggregates. Resonance Raman and photocurrent imaging of model P3ATV/fullerene blend solar cells were next performed to spatially correlate local morphology to photocurrent generation efficiency. Raman images of aggregated and amorphous P3ATV regions were constructed that show larger photocurrent production in the former, suggesting these structures are well mixed with PCBM. Conversely, amorphous zones have diminished PCBM content, resulting in lower photocurrents. Absorption and Raman spectra demonstrate that the P3ATV aggregate packing characteristics and amounts are largely unaffected by the addition of PCBM, indicating weak interactions with P3ATV chain backbone that lead to poor charge generation efficiencies in solar cells.

Raman Spectroscopy of Organic-Inorganic Halide Perovskites.

Micro-Raman spectroscopy provides laterally resolved microstructural information for a broad range of materials. In this Letter, we apply this technique to tri-iodide (CH3NH3PbI3), tribromide (CH3NH3PbBr3), and mixed iodide-bromide (CH3NH3PbI3-xBrx) organic-inorganic halide perovskite thin films and discuss necessary conditions to obtain reliable data. We explain how to measure Raman spectra of pristine CH3NH3PbI3 layers and discuss the distinct Raman bands that develop during moisture-induced degradation. We also prove unambiguously that the final degradation products contain pure PbI2. Moreover, we describe CH3NH3PbI3-xBrx Raman spectra and discuss how the perovskite crystallographic symmetries affect the Raman band intensities and spectral shapes. On the basis of the dependence of the Raman shift on the iodide-to-bromide ratio, we show that Raman spectroscopy is a fast and nondestructive method for the evaluation of the relative iodide-to-bromide ratio.